Reddit user Cherieish posted this story last month, as far as I can tell. I think that's really cute!
My three-year-old son loves Doctor Who. He decided that the Doctor is the one who brings Christmas presents, not Santa. So of course, last Christmas, we decided to get him a sonic screwdriver "from" the Doctor, along with a letter saying that this was his very own sonic screwdriver, but he got a new one so he's giving this one to my son. He loved it.
A few weeks later, we went on vacation and the screwdriver got misplaced somewhere. We knew he'd be heartbroken, so we told him that the Doctor had borrowed his screwdriver back for a few days (while I ordered a new one from Amazon).
After it arrived, we waited until my son was in bed, placed the screwdriver with a note ("Thanks for letting me borrow it!") outside his bedroom door, then played the TARDIS sound on my computer speakers. He came running out and found the screwdriver that "the Doctor" had "brought back."
He talks about it all the time.